Method of laying armoured cables



Oct. 20, 1959 D. SHORT METHOD OF LAYING ARMOURED CABLES 2 Sheets-Sheet 1 Filed Dec. 14; 1955 Inventor HERBERT 0. SHORT 9Z7 Att ys H. D. SHORT METHOD OF LAYING ARMOURED CABLES 2 Sheets-Sheet 2 Filed Dec. 14, 1955 Inventor HERBERT D. SHORT By: 0/2 41 z Att' ys FIG.4

United States Patent METHOD or LAYING ARMOURED CABLES Herbert Douglass Short, Toronto, Ontario, Canada, as-

signor to Canada Wire and Cable Company Limited, Toronto, Canada, a corporation This invention relates to the laying of long lengths of armoured cable, for example, armoured subaquatic cables, in which the armour is formed by a plurality of wires wound helically round a core of the cable. The invention is specifically concerned with overcoming the problems of breakage of ferrules used for joining lengths of the conductor together due to the development of excessive tensile stresses in the conductor, and birdcaging, which problems have existed since the beginning of the art, and which have hitherto not been satisfactorily solved.

An object of the invention is to provide a method of arranging an armoured, cable in a plurality of flakes, in which the stresses set up in the cable result in a predominately compressive stress being applied to the conductor in the direction of its axis.

A further object of the invention is to provide an improved method of ararnging an armoured cable in a plurality of flakes in a manner in which the formation of birdcages in the armour is prevented.

A still further object is to eliminate, or at least mitigate, the possibility of fractures occurring in ferrules within the cable used for joining together portions of the conductor.

Throughout the following description the term righthand, as applied to the direction of helix of a winding of the cable, i.e., the conductor or the armour, means that when the cable is Viewed along its axis the helix recedes from the eye in a clockwise and axial direction. Conversely, the term left-hand means that the helix recedes from the eye in an anticlockwise and axial direct-ion.

By flake is meant a flat Archimedean spiral formed in a substantially horizontal plane by coiling the cable, the words clockwise and anticlockwise as applied to the direction or hand of coiling of the cable to form a flake indicating the direction of coiling of the cable when viewed from above, and starting at the outer periphery of the coil.

By birdcage is meant a localized increase in the pitch diameter of the helix of the armour wires.

According to the invention, the method of laying armoured sub-aquatic or submarine cables includes the steps of determining the hand of the armour wires, and coiling the cables on a substantially horizontal surface into an Archimedean spiral the hand of which, when viewed from above, is the same as the hand of the armour wires, the cable'being coiled from the maximum diameter of the spiral to the minimum diameter, whereby tensile stresses predominate in the armour as opposed to compressive ones.

The advantages of the method of the invention will be appreciated by a study of the specification when taken in conjunction with the accompanying drawings.

Figure l is a perspective view of a left-hand armoured cable, showing various insulating, waterproofing and armouring coverings stripped back to expose the inner coverings and the conductor.

Figure 2 is a diagram indicating the manipulation of the cable up to the point of it being laid;

2,909,336 Patented Oct. 20, 1 959v ice,

Figure 3 is a diagrammatic perspective view of a cable in the process of being coiled; and

Figure 4 is a diagram indicating theoretical rotation of a cable about its axis when it is coiled.

Armoured cables which are to be laid under rivers or on a sea bed commonly, if not universally, have a form which is basically that shown in Figure 1, although they may be subject to various modifications in detail.

In Figure 1, the current carrying conductor 10 consists of a bunch of metal filaments formed of, for example, copper, aluminum, or their alloys, or a combination of them with other materials, the conductor being wrapped or encased in layers of fabric, rubber, and/ or layers of impregnated paper, two layers of which are indicated at 11,12. A sheath 13 of lead is swaged or extruded over the layers 11, 12, the sheath forming a water-impervious barrier protecting the layers of insulation.

Servings of bitumen impregnated jute, indicated at 14, are wrapped round the sheath 13 and form a bedding for the cable armouring, which armouring is formed by a plurality of parallel metal wires 15 ararnged in a helix round the concentric coverings of the conductor with adjacent wires in contact with each other. The armour wires are formed from any suitable high-strength metal, and their purpose is, apart from protecting the conductor and its coverings in a radial direction, to form the structural element of the cable construction and thereby support the cable core when pulled or suspended in air or water so as to relieve the conductor from the longitudinal stresses to which the cable may be subjected when being laid or otherwise handled, or in use.

The armouring may be encased with servings of bitumen impregnated jute which form a protective 16 over the armour wires.

The invention is not concerned however with the specific form or the materials from which the cable is formed, except in so far as the armour consists of a plurality of parallel metal wires which are arranged helically around the protective coverings of the conductor.

Referring now to Figure 2, which indicates diagrammatically the various steps in the manipulation of the cable 20 up to the time it is laid, the conductor 10 and its insulating and waterproofing coverings 11 to 14 are prefabricated as is indicated by the block 21, and the armouring 15 and covering 16 is subsequently applied in a machine of known construction which is indicated by the block 22. The cable is then coiled into a flake on a suitable location, such as a clock 23, from which the cable is to be loaded into the hold of a cable-laying ship or other Vessel indicated at 24.

As the cable emerges from the armouring machine 22, it is passed along gantries 25 to a selected position and is there coiled into a flake as is indicated at 26, after which it is passed over gantries 27 and again coiled into a flake in the hold of the cable-laying ship, or other 'vessel, as is indicated at 28, the cable then being payed out by means of the usual gear, indicated at 29, and laid on the river or sea bed.

As is indicated by Figure 3, each flake is formed by securing the free end 20a of the cable 20, as is indicated at 20b, to prevent rotation of that end of thecable and coiling from the maximum diameter 30 to the minimum diameter 31, after which spacers 32 .are placed on the flake and the cable is passed outwardly at 200 between the spacers to the maximum diameter and is coiled into a further flake overlying the previously formed one. In this way the cable is formed into a plurality of flakes which are stacked one on the other, the procedure being repeated until such time as sufficient cable to load the its own weight thereby preventing the cable whipping out of alignment as the flake is formed, and subsequent inner turns of the coil are located by the adjacent outer turns. Also, when flaking onto the dock, the cable. is rigidly held at its end remote fromjrhe coil, by the machine which is providing the armouring.

Referring now to Figure 4, if one considersthe behaviour of an armoured cable when it is formed into a flake, the cable being held .at someremote point in a manner preventing rotation of the cable about its axis at that point, it will be found that each turn of the cable in each flake will rotate about its longitudinal axis approximately 1 degree for each 1 degree subtended by the are of the cable in said turn. Thus, if the arc of the cable in each turn subtends an angle a of 360, the end of the cable will have rotated through approximately 360 in a direction which is of the same hand as the are, as is indicated at b, i.e., if the coil is wound in an anticlockwise direction, as is shown in the drawing, the rotation of the cable in each turn about its longitudinal axis will be in an anticlockwise direction, or, if the coil- 4 ing is in a clockwise direction, the rotation of the cable in each turnabout its axis will be in a clockwise direction also, and in each case the angle through which the cable rotates will be substantially the same as the angle subtended by the arc of the cable.

The practice was established some ninety or more years ago that a left-hand cable (i.e., one in which the armour wires were wound in an anticlockwise direction on the conductor sheath) should be coiled in a clockwise direction, and, conversely, a right-hand cable should be coiled in an anticlockwise direction. The reasons for following this procedure are lost in antiquity but hitherto the procedure has been closely followed and it has not been appreciated that the inherent disadvantages in the method can be overcome.

The main disadvantage of the method of the prior art resides in the fact that when, for example, a right-hand cable is coiled in an anticlockwise direction the torsional forces developed in the cable during the coiling are in the opposite direction to the direction of helix of the armour winding, as will be evidenced by examination of Figure 4, i.e., the winding of the armour is clockwise and the torque is in an anticlockwise direction. Identical conditions arise when a left-hand cable is coiled. in a clockwise direction.

The torque in the cable is taken almost exclusively by the armour wires, with a consequence that the armour attempts to unwind, the torque developing compressive stresses in the armour wires which attempt to relieve themselves either by increasing the length of the armour by increasing the pitch of the helix, or by increasing the mean diameter of the helix of the armour. In the former case the result is the setting up of high tensile stresses in the conductor, which is not intended or designed to withstand such stresses, with consequential stretching of the conductor or more usually the fracturing of any ferrule used to join portions of the conductor together. In the latter case the result is localized bursting of the covering 14 surrounding the armour with a consequence that the stresses are locally relieved by the mean diameter of the armour increasing at the burst and resulting in a birdcage. In both cases, which tend to occur in combination, the cable is severely damaged and is either inoperative or subject to rapid deterioration when laid.

This condition is further aggravated by the fact that the cable, after being coiled on the dock, has then to be transferred to and coiled into the hold of a cable laying ship or other vessel. The stresses in the cable are relieved as the cable is uncoiled from the flakes on the .dock and passed over gantries into the ship, but are 4 restored as the cable is coiled into the hold of the ship.

The above disadvantages are avoided by the method of the present invention by coiling a cable having lefthand armour in an anticlockwise direction, or a cable having a right-hand armour in a clockwise direction. In the method of the invention, the torque acts in the same direction as the winding of the helix, as will be evidenced by examination of Figure 4, and results in a tensional stress being set up in the armour (which is designed to Withstand such stresses) due to the tendency of the armour to wind up and .the pitch of the helix of the winding to decrease, thus subjecting the conductor to a compressive stress as opposed to a tensile one.

In this way the formation of birdcages in the armouring is avoided, and is in fact impossible, and there is no danger of fracturing any ferrule in the conductor, or of excessive tensile stresses developing in the conductor. Also, as the tendency of birdcaging due to internal stresses is eliminated, there is less possibility of small and unnoticed fissures being formed in the bitumen impregnated jute.

It will be appreciated that when a cable is bent to form an arc, stresses are set up in addition to those resulting from a rotation of the cable about its axis, the stresses at any particular point along the axis being perpendicular to the radius subtending the are at that point. These stresses set a minimum permissible radius to which the cable can be coiled, but otherwise are not of great consequence and are of a minor order as compared to the stresses setup due to rotation of the cable about its axis.

What I claim as my invention is:

1. The method of flaking a cable having an electrical conductor, a sheath of insulating material surrounding the conductor, and armour wires wound helically around the insulating sheath, each and every armour wire being of the same hand of winding when viewed axially of the cable, said method comprising passing the cable downwardly onto a stationary, substantially plane horizontal surface, and coiling it on said surface in .an Archimedean spiral, holding the leading end of said cable against rotation about its longitudinal axis and the coil immovable relatively to said surface, the coiling being of a hand which is the same as the hand of the armour wires.

2. The method of flaking a cable having an electrical conductor, a sheath of insulating material surrounding the conductor, and a series of armour wires wound helically around the insulating sheath for each wire of the series to be of the same hand .of winding when viewed axially of the cable, said method comprising passing the cable downwardly towards a horizontal surface in a direction substantially perpendicular thereto and then in a direction which is substantially parallel to said horizontal surface, holding the cable against rotation about its longitudinal axis at its end lying in said horizontal plane and at a position remote from said end and which inc'ludes that portion of the cable which is substantially perpendicular, and coiling the cable on the said substantially horizontal surface in an Archimedean spiral of a hand which is the same as the hand of the armour wires.

References Cited in the file of this patent UNITED STATES PATENTS 1,230,009 Mirfield 'et al. June 12, 1917 2,203,435 Kempe June 4, 1940 2,419,241 Wingate Apr. 22, 1947 2,709,553 Wellcome May 31, 1955 FOREIGN PATENTS 21,660 Great Britain Oct. 8, 1904 606,752 Great Britain Aug. '19, 1948 

